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pgmedge - edge-detect a portable graymap
pgmedge [pgmfile]
Reads a portable graymap as input. Outlines the edges, and writes
a portable graymap as output. Piping the result through pgmtopbm -threshold
and playing with the threshold value will give a bitmap of the edges.
The
edge detection technique used is to take the Pythagorean sum of two Sobel
gradient operators at 90 degrees to each other. For more details see "Digital
Image Processing" by Gonzalez and Wintz, chapter 7.
The maxval of the output
is the same as the maxval of the input The effect is better with larger
maxvals, so you may want to increase the maxval of the input by running
it through pnmdepth first.
pgmenhance(1)
, pgmtopbm(1)
, pnmdepth(1)
,
pgm(5)
, pbm(5)
Copyright (C) 1991 by Jef Poskanzer.
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